✍ Worked-example 6.3(a)Predict the products of electrolysis of lead (II) nitrate solution at anode and cathode.Solution

Aqueous solution

At anode (+)

At cathode (-)

Movements of ion to electrode

NO3-, OH-

Pb2+, H+

Ion selected for discharged

Ion OH- selected for discharged as it is lower position in electrochemical series.

Ion H+ selected for discharged as it is lower position in electrochemical series.

Half-equation

4OH- → 2H2O + O2 + 4e-Oxygen gas is collected

2H+ + 2e- → H2Hydrogen gas is collected

Concentration of ions in electrolyte solution
■ Concentration of ions in electrolyte solution

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An ion will be selected for discharge, when the concentration of a particular type of ion is high.

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Usually, in the electrolysis of concentrated halide solution [Cl-, Br-, I-], the concentration of the halide ion is always higher than the hydroxide ion, OH-. Thus, halide ions will be discharged at the anode.